Studied by 18 peopleHeritable traits are controlled by?
They are controlled by genes that are carried on chromosomes.
Changes in genes and chromosomes produce?
These changes produce variation.
What do all organisms have that is "invisible"?
All organisms have additional genetic variation that is "invisible" because it involves small differences in biochemical processes.
Define population.
A group of individuals of the same species that interbreed.
What does natural selection act on?
It acts on an organism's phenotypes, not directly on its genotype.
What type of phenotypes dominate?
Favorable phenotypes dominate.
Who do individuals with favorable phenotypes pass their genes onto?
They pass their genes onto their offspring.
What does a gene pool consist of?
It consists of all genes, including all the different alleles present in a population.
What determines genetic variation in a population?
The gene pool determines genetic variation in a population.
What is allele frequency?
It is the number of times that an allele occurs in a gene pool.
What is evolution in genetic terms?
In genetic terms, evolution is any change in the allele frequency of alleles in a population.
True or false: Populations evolve, not individuals.
True: Populations evolve, not individuals.
What are the 3 main sources of genetic variation?
The 3 main sources are mutations, gene shuffling (meiosis), and lateral gene transfer.
What are mutations?
They are changes in a sequence of DNA that must occur in gametes (sperm and egg) and can be good, neutral, or bad. They can increase or decrease fitness as well.
What are the 2 circumstances that cause gene shuffling (meiosis)?
The 2 circumstances are independent assortment and crossing over.
What does lateral gene transfer mean?
It means that some species (like bacteria) transfer genes from one to another.
What is a single-gene trait?
It is a trait controlled by a single gene that has 2 alleles (dominant/recessive).
What is a polygenic trait?
It is a trait controlled by 2 or more genes.
Modern pesticides used to kill most insects, but after a few years, many stopped working. Why?
Genetic variation allows for pesticide resistance, and that resistance is passed onto offspring. Thus, populations evolve, and pesticides no longer work.
Natural selection on single-gene traits can lead to?
They can lead to changes in allele frequencies in a population, leading to evolution.
In what 3 ways can natural selection on polygenic traits affect the distributions of phenotypes?
The 3 ways are directional selection, stabilizing selection, and disruptive selection.
What is directional selection?
It is when individuals at one end of the population curve have higher fitness.
What is stabilizing selection?
It is when individuals near the center of the curve have higher fitness. Intermediate forms of a trait are favored and alleles that specify extreme forms are eliminated from a population.
What is disruptive selection?
It is when individuals at the extremes of the curve have higher fitness. Selection creates 2, distinct phenotypes.
Define speciation.
Formation of a new species.
Define reproductive isolation.
When members of a species stop breeding with one another.
What does reproductive isolation cause the gene pool to do?
It causes the gene pool to split, creating 2 new species.
Due to what 3 Reproductive Isolating mechanisms does speciation occur?
The 3 mechanisms are behavioral isolation, geographic isolation, and temporal isolation.
What is behavioral isolation?
It is when populations that are capable of interbreeding choose not to because of courtship rituals or other behaviors.
What is geographical isolation?
It is when physical barriers such as mountain ranges and oceans prevent breeding. Natural selection may act on each separate group in separate ways, and separated groups can no longer mate after an extended period.
What is temporal speciation?
When 2 or more species reproduce at different times.
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